Offshore oilfield development faces complex geological conditions and high development costs, with limited platform lifespans and well locations. These constraints reduce the effectiveness of chemical flooding for enhancing oil recovery. Based on the geological characteristics of offshore oilfields, and drawing on the results of synergistic enhanced oil recovery (EOR) techniques combining chemical flooding and infill well patterns in Daqing, Dagang, and Shengli oilfields, this study evaluates the synergistic potential of chemical flooding agents, well pattern infill, and layer adjustment. The synergy between chemical flooding and infill well pattern optimization for enhanced oil recovery was established. Relying on numerical simulation, an optimized design for synergistic chemical flooding and infill well patterns was developed for the SZ36?1 oilfield. The effects of reservoir permeability, permeability heterogeneity, and crude oil viscosity on enhanced oil recovery potential were clarified, along with the establishment of corresponding boundaries. The study demonstrated that after the original inverted nine?spot well pattern is encrypted into an oblique inverted nine?spot well pattern, the well spacing is reduced by half. Combined with polymer flooding technology, the recovery rate can be increased by 9.8%, which is 3.4% higher than the sum of the recovery increases achieved by independent water flooding and polymer flooding. This result confirms that by utilizing the synergistic effect of chemical flooding and infill well pattern technology in offshore oilfields, the sweep efficiency of the oil displacement system can be significantly enhanced, leading to a substantial increase in recovery rates and optimization of production capacity.